1. Field of the Invention
The present invention relates to a material used for surface-treating base members or coating films provided on base members, and a method for forming thin-films as such a surface treatment.
2. Description of the Related Art
Conventionally, for surface-treating various base members or substrates, a thin-film which is stain-proof, water-, dust-proof, etc. made from organic materials, etc. is formed onto the surface of the base members so that the surface acquires those same properties. To form such a thin-film, for example, Japanese Patent Application Laid-Open No. 60-40254 discloses a method of directly applying a water-repellent substance diluted in an organic solvent onto an under-coating layer formed on a base member Japanese Patent Application Laid-Open No. 61-130902 discloses a method of dipping a base member (lens) in a solution of a water-repellent substance. In addition, Japanese Patent Application Laid-Open No. 4-72055 discloses a method of forming a protective film on a base member by evaporating an organic substance impregnated in a porous ceramic material in a vacuum chamber and then depositing the evaporated substance on the base member. Japanese Patent Application Laid-Open No. 6-340966 discloses a method of forming an organic film on an inorganic coating film by evaporating an organic substance impregnated in a fibrous metallic mass in a vacuum chamber and then depositing the evaporated substance on the inorganic coating film.
However, such film-forming methods have the following problems:
By directly applying a water-repellent substance onto a base member, a sufficiently uniform coating film cannot always be obtained. In particular, when a water-repellent substance is applied onto an inorganic thin-film formed by vacuum processing, such as vacuum deposition, it is necessary to remove a base member from a vacuum chamber after forming an inorganic film on the base member by vacuum deposition, and then, to subject the base member to another step in order to be coated with the water-repellent substance. Thus, the process as a whole becomes complicated and uneven coating readily occurs. As a result, it is difficult to achieve a uniform water-repellent thin-film.
The dipping method requires a similar complicated process, in particular when a water-repellent substance is applied onto an inorganic thin-film formed by vacuum processing. Furthermore, since the required amount of the diluted solution of the water-repellent substance is much greater than the actual coating amount, additional equipment and cost are necessary for waste-liquid disposal.
According to the method of evaporating an organic substance impregnated in a ceramic material, steps such as pressing and high-temperature sintering are required for forming the ceramic material. Also, the porosity of the ceramic material must be finely adjusted to control the amount of the impregnated organic substance. Therefore, it is necessary to strictly control the grain size, sintering temperature, purity, etc. of the ceramic material, and correspondingly, the process for material preparation becomes more complicated and the cost increases. In addition, organic binders are frequently used for preparing ceramic materials. Thus, when organic substances (the organic binders or decomposed products thereof) remain in a ceramic material, they react or evaporate with the film-forming material (e. g., a water-repellent substance such as an organic silicone or a perfluoroalkyl-group containing compound) impregnated in the ceramic material and are deposited on the subject, i. e., base member. Thus, the properties of the resulting thin-film deteriorate, such as reduced contact angle, and the desired properties such being dust-proof and water-proof cannot be achieved.
The method of evaporating an organic material impregnated in a fibrous metallic mass is simpler than the above-mentioned other methods. However, in particular, when metals having a melting point of from 600.degree. C. to 800.degree. C., such as copper and aluminum, are used, the metallic mass may start melting under certain heating conditions or the melted metal per se may evaporate and adhere to the base member, resulting in adverse effects on the properties of the resulting thin-film, such as coloring or reduced contact angle. In addition, since metals have high thermal conductivity, their rate of temperature rise is high. Thus, in some cases, evaporation of the impregnated organic substance must be carefully adjusted.